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The invention relates generally to industrial control systems, and more specifically to an industrial control system having a battery backed solid-state memory, the battery preventing loss of data during momentary power interruptions.
Industrial controllers are special purpose computers used for the control of industrial processes and the like. While executing a stored program, they read inputs from the controlled process and, according to the logic of a contained control program, provide outputs to the controlled process.
Industrial controllers differ from regular computers both in that they provide xe2x80x9creal-timexe2x80x9d control (i.e., control in which control outputs are produced predictably and rapidly in response to given control inputs) and in that they provide for extremely reliable operation. In this latter regard, the volatile memory used by the industrial controller is often backed up with a battery so that data needed for the control program is not lost during momentary power outages. Volatile memory is that which requires power to maintain its stored data.
Such xe2x80x9cbattery backedxe2x80x9d memory, using a combination of static random access memory (SRAM) and a long life battery such as a lithium cell, is well known. In current control applications, synchronous dynamic random access memory (SDRAM) may be preferred to SRAM because of its higher density, faster speed, and lower cost. Unfortunately, the amount of power needed for SDRAM can be thirty times greater than that needed for conventional SRAM devices. The voltage requirements of SDRAM require that the lithium cell voltage be stabilized with a DC-to-DC converter, introducing additional power losses of about 25 percent. High speed SRAM is one alternative, but high-speed SRAM still draws about ten times as much current as the older SRAM devices, has much lower density than SDRAM in number of bits of storage per device, and costs much more than SDRAM per device.
Many customers wish to disconnect power from their industrial controllers during the night, over weekends, and during scheduled factory shutdowns. The high power requirements of SDRAM and high speed SRAM produce unacceptable battery drain in these situations. At times, it may be desirable to ship an industrial controller preprogrammed from the factory. The one-month or more of transport time make battery back-up of the programmed data impractical.
The present invention allows automatic deactivation of the battery backup for periods of planned power outage. In this way, memory devices having high power consumption may be provided with battery back up during short periods of unexpected power loss, without risk of high battery discharge levels during longer scheduled shutdowns. The invention may include nonvolatile (e.g., Flash) memory into which selected data from the volatile memory may be saved prior to a planned shut down.
Specifically, the present invention provides a battery backed memory system having a first line receiving a source of line voltage and a second line receiving a source of battery voltage to provide backup voltage when the line voltage is lost. A volatile solid-state memory receives voltage from the first line, and from the second line via an electronically controlled switch. A microprocessor communicating with the volatile solid-state memory and the electronically controlled switch, executes a program to open the electronically controlled switch in response to a signal indicating a planned cessation of line voltage.
Thus it is an object of the invention to distinguish between and respond differently to power outages that are unexpected and that require battery backup and those which are planned in which battery backup may not be required.
The system may further include nonvolatile solid state memory communicating with the microprocessor and the executed program may operate to transfer predetermined data from the volatile solid state memory to the nonvolatile solid state memory in response to the signal indicating a planned cessation of line voltage and prior to opening of the electronically controlled switch.
Thus it is an object of the invention to allow storage of data in nonvolatile memory when a planned power outage is incurred, thus eliminating loss of critical data, and to allow for such a transfer while line voltage is present to ameliorate the power demands of programming common non-volatile memories.
The invention may include a latch connected between the microprocessor and the electronically controlled switch so that the electronically controlled switch is latched open even after loss of power to the microprocessor.
Thus it is another object of the invention to allow the microprocessor to be fully powered down during loss of line voltage without affecting the disconnection of the battery from the volatile memory.
The invention may include circuitry for resetting the latch upon restoration of line voltage to the first line.
Thus it is another object of the invention to ensure that battery backup is reestablished on next power up after an unplanned power outage without the necessity of resetting by the microprocessor.
The volatile memory may include static and dynamic random access memory.
Thus it is another object of the invention to provide a system that works not only with high current dynamic memories but also faster, higher current static memory systems.
The system may include a DC-to-DC converter for use with the dynamic access memory and a voltage regulator for use with the static memory.
Thus it is another object of the invention to provide improved battery backup operation for memory systems that include efficiency decreasing, regulation, or DC-to-DC conversions.
The foregoing objects and advantages may not apply to all embodiments of the inventions and are not intended to define the scope of the invention, for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose.